New quantitative techniques will be applied for the detection of antibodies in serum against human neutrophils and other leukocytes. The method concerns the detection of opsonic antibody against cells by measuring the metabolic response of phagocytes attempting to ingest the sensitized cells. The specific applications of the new method include: 1) the search for autoantibodies in serum of patients with "idiopathic" and drug-associated neutropenia; 2) the definition of antigens on human neutrophils by testing for reactivity of neutrophils against sera of patients transfused because of cancer and hematologic disorders; 3) the cross-matching of patients receiving leukocyte transfusions (because of pancrytopenia associated with cancer or other causes of bone marrow failure) and donors of the leukocytes. Further definition of neutrophil antigens and validation of a leukocyte cross-matching procedure are important prerequisites in establishing the practicality of leukocyte transfusions in the support of cancer patients.